1. Field of the Invention
This invention relates to a cowling structure for a marine propulsion engine and, more particularly, to an improved cowling structure for permitting the induction of air for engine operation while inhibiting water from entering the engine compartment.
2. Description of Related Art
A protective cowling of an outboard motor normally contains a powering internal combustion engine of the motor. The cowling insures that the engine and its auxiliaries do not become wet and subject to corrosion. At the same time, however, it is also necessary to provide atmospheric air to the engine for combustion and/or for cooling of the engine and its components. Because the engine requires substantial amounts of airflow for its combustion process, it is necessary to provide air openings in the protective cowling through which air may be drawn from the atmosphere. A wide variety of air induction systems have been proposed for outboard motors which serve the main purpose of providing ample air flow to the engine for combustion while separating water from the inducted air to reduce corrosion and to inhibit the possible fouling of the engine.
Generally, it has been the practice to provide an air inlet opening at the upper rear portion of the cowling through which atmospheric air can be drawn for engine combustion. Such an inlet opening is normally formed in the cowling and opens upward to permit atmospheric air to flow into the interior of the cowling.
The inlet opening also faces rearward so that water splashing and spraying during the operation of the watercraft will not enter the cowling through the opening. The rearward facing air inlet opening, however, can cause a problem in that, when the watercraft is suddenly decelerated, water may splash up and enter the opening.
In addition, normally some form of baffling or labyrinthine type flow arrangement is provided in the inlet device for assisting in separating water from the air that is passing into the interior of the protective cowling. Although such an arrangement can provide some assistance in reducing the flow of large amounts of water into the interior of the protective cowling, this type of construction can actually facilitate the entry of smaller amounts of water into the engine in the form of droplets or spray. This is because baffling arrangements typically increase the airspeed of the intake air, which results in a greater tendency for water to remain suspended in the rushing air, rather than precipitate out of air flowing into the cowling. Moreover, water droplets commonly condense on the surfaces of the labyrinth passages, and are drawn into the protective cowling and deposited upon the surface of or ingested by the engine. In an addition, these complicated configurations are very expensive to manufacture and/or require multiple pieces for the protective cowling.
Certain portions of the engine are more prone to attack from corrosion and damage from the water than others. For example, the ignition system including the spark plugs, spark coils and spark wires, can be seriously affected if water impinges upon them. Misfiring can occur or in extreme situations the actual running of the engine can be interrupted. In a similar manner, the charge forming system (e.g., a carburetor and/or throttle arrangement) can be subject to deterioration if water impinges upon it. Of course, these problems are particularly aggravated if the engine is operated in a marine environment since the salt water will cause more corrosion than fresh water.
While it is possible to restrict the size of the openings in the protective cowling and thereby reduce the total amount of water traveling into the protective cowling, such restrictions would result in higher airspeeds of atmospheric air drawn into the restricted opening. This consequently increases the amount of suspended water ingested by the engine as described above. A restricted air passage can also significantly reduce engine performance, particularly under wide-open, full-throttle conditions.